Encouraging young writers is laudable. After all, it’s increasingly difficult to get started. Publishers’ advances are low and getting lower; arts degrees are more expensive than Stem subjects; social security is fiercely tested. Which must mean that those most able to pay for a writing course, or those most able to take time off work to write while still young, are those most likely to have money, security, contacts, confidence. There’s a correlation between setting an age bar and encouraging the already privileged.

All writers were young once, and many start writing young, but not all begin their careers as published authors at that point. Leaving aside the fact that some only decide to start writing later in life, many factors affect one’s ability to commit to writing seriously. Besides income issues, age bars can lead an organisation into worrying territory. Authors from outside the perceived cultural mainstream who do not already see their voices represented – LGBTQ writers, writers of colour – are sometimes slow to recognise the contribution they can make, or to feel like their voices will be valued.

Age is a feminist issue. Carers, delayed by years looking after children or other dependents, are mostly women; residencies that offer no childcare or require long stays are an easy way to sift female candidates out of contention. Older women are already told every day, in ways ranging from the subtle to the blatant, that they are irrelevant and should shut up. Multiply this by, say, race or gender, and the courage required to put work out is even greater. Or the potential writer might not be the carer, but the cared-for. Writers who live with a disability or ill-health may not start out until they have found a way to write with their condition – which may take longer than this 40-years-old rule allows for.

Since writing to the RSL, I’ve been sent heartrending accounts from well-published writers, several of whom specified that it wasn’t until their late 30s that they were finally able to take the time to write, making age bar of 40 not only arbitrary, but a particularly cruel irony. Some writers “emerge” despite challenges, and they should be celebrated – but it is unreasonable to put arbitrary barriers in the way of less privileged applicants and expect them to perform better than those more advantaged.

The EU Employment Equality Framework Directive establishes general guidelines for fair treatment. It “aims to protect everyone in the EU from discrimination based on age, disability, sexual orientation and religion or belief in the workplace”. Writers, who earn so little on average, rely on awards and residencies as income as well as validation. Age-based criteria work against the spirit, if not the letter, of this directive.

Over-40s are barred from many prizes already. Despite the Royal Society’s good intentions to increase the narrow age range of their fellows, an arbitrary cut-off point contributes to an atmosphere of exclusion, something the Turner prize realised when it abandoned its under-50 stipulation this year. The intersections of ageism for the young and old are complex and could be better addressed via a variety of initiatives, which could include proper research combined with outreach. Disadvantaged young writers need support and development; not a cutoff point at precisely the age many of them finally reach publication.

Rereading my original piece about ageism, I feel I could have written more forcefully. But I was a “new” writer and I lacked the confidence that has since come with the validation I’ve gained, partly through being awarded residencies, the occasional grant and even one prize. I no longer need to be so polite. I am angry. Make no mistake: if you run a prize, a “best of” list, a residency, with age guidelines you can’t fully justify then, however otherwise diverse your awardees, you and your organisation are consolidating racism, sexism, class and gender discrimination. I know you don’t want that. The good news is that it’s so easy to replace the word “young” with “new”. If you run a prize or scheme, be a hero: with just one word changed, a whole wall disappears. Do it, do it today.

• Joanna Walsh’s latest book is Worlds From The Word’s End. She is the 2017 Arts Foundation Fellow for Literature, and runs @read_women.